The present invention relates to a manifold adaptor plate that functions as a gasket utilized to separate filtrate from feed and retentate in a tangential flow filtration apparatus. More particularly, this invention relates to such a manifold adaptor plate of unitary construction having a plurality of layers including one or two sealing layers and an intermediate rigid support layer.
Prior to the present invention, liquids, primarily aqueous liquids, have been filtered by tangential flow modules wherein a plurality of filters are stacked between two manifolds, one at the bottom of the stack and one at the top of the stack. The filtration module stack comprises a collection of one or more filtration modules and associated intermodule gaskets. The filters are separated by appropriate screens and liquid-impervious layers to permit liquid flow as well as filtrate and retentate flow into and from the stack. In addition, flow holes are provided through the layers within the stack. The holes are sealed appropriately with a separate sheet of gasketing material to prevent admixture of filtrate with incoming liquid feed or retentate. The manifolds in each segment are designed so that filtrate is removed from the second manifold. This manifold arrangement necessitates fittings to both manifolds in order to supply and remove liquid to and from manifolds in order to supply and remove liquid to and from the stack. This can be undesirable since additional manipulative steps for removing and connecting the fittings are required when it is desirable to replace the filtration elements forming the stack.
Alternative tangential flow modules are disclosed in U.S. Pat. Nos. 5,176,828 and 5,597,447 wherein a single manifold is utilized at one end of each stack of filters and a plate is positioned at the opposite end of each stack of filters. Liquid flow paths are provided to assure that filtrate is not contaminated with either retentate or feed.
In the tangential flow modules described above, a separate sheet of gasket material is positioned between the one or two manifolds and the stack of filters to assure the desired liquid flow. The gasket sheet, is used with manifold adaptor plate consists of a metal plate. The elastomeric gasket sheet, such as silicone, can be placed against each surface of the metal plate to provide desired sealing. The metal plate and elastomeric gasket sheets are provided with liquid flow paths to assure the desired liquid flow to, within and from the tangential flow module.
The use of a manifold adaptor plate having a separate elastomeric sheet layer is undesirable, since, due to its flexibility, it is difficult to properly align the liquid flow paths through the elastomeric layer with the liquid inlets and liquid outlets of the manifold. In some instances it is possible to deform the gasket sheet during application in such a manner to allow for the improper mixing of fluids. In addition, the elastomeric layer tends to stick to the manifold causing wrinkling that adversely affects uniform and complete contact with the manifold surface. This condition can lead to external leaks as well as imperfect alignment of liquid flow paths that can cause cross contamination of flowing liquids. In addition, when the elastomeric gaskets are compressed during use of the module, they tend to move which can cause significant liquid inlet and liquid outlet distortion. The separate sheet is generally formed of silicone which has relatively high extractables that can be adding to the fluid that passes through it. These extractables need to either be removed from the fluid before use or to be tested to ensure they don't contaminate or otherwise cause an adverse reaction in the final product, particularly when it is a drug or therapeutic protein. Lastly, the gasket sheet being a relatively weak and unsupported structure formed of relatively low durometer silicone or rubber, it can tear during handling and storage rendering it useless and they can distort enough to cause an external leak as well.
Accordingly, it would be desirable to provide a manifold adaptor plate which provides satisfactory sealing without the liquid flow path alignment or handling problems of the prior art.